The invention relates to electronically controllable radio frequency phase shifters.
In the prior art, electronically controlled phase shifters have been applied, particularly in radar systems. In fact, the evolution of phased array radar has been made possible, at least in part, by the development of electronically controlled inertialess phase shifters. Such phase shifters are now extensively employed in phase-scanning systems. Both the existing types of phase shifters and the radar systems themselves are extensively described in the technical and patent literature. The text, RADAR HANDBOOK, by Merill I. Skolnick (McGraw-Hill Book Company, 1970), provides a background in respect to such systems, particularly in Chapter 11 thereof. Chapter 12 of the same handbook is devoted to "phase shifters for arrays", the state of that art being therein summarized. It will be noted therein that the types of phase shifters known and used in the radar art have taken several forms. One, the so-called "twin-slab" phase shifter, employs a ferrimagnetic toroid within a waveguide with control magnetizing (drive) means associated therewith. Such phase shifters can be built in purely analog form or in successive sections of properly scaled phase shift significances so that they may be separately controlled in accordance with a digital control format. Other ferrimagnetic type phase shifters include the so-called Reggia-Spencer configuration and various forms of strip-line combinations with ferrimagnetic material associated therewith. Still further, strip-transmission-line slow-wave-structure phase shifters are known and discussed in the referenced handbook. Other forms and variations of the electronically controlled phase shifter genera are also described in Chapter 12 of the aforementioned handbook.
It is generally conceded that high-power phase shifters are inherently difficult to construct, are expensive, and exact penalties in terms of size, weight and system inefficiency.
Another type of phase shifter is the so-called diode and strip-line digital type. One form of such a device is described in U.S. Pat. No. 4,044,360. That device includes an additional feature making the phase shifter retro-directive, as well as forward transmissive, selectively.
The manner in which the present invention improves upon the shortcomings of many of the prior art approaches to the problem of electronically controlled RF phase shifting will be evident as this description proceeds.